Field of the Invention
The invention relates to technologies for eliminating impulse interference.
Description of the Related Art
With the progress in communication technologies, the development of digital television broadcasting has also gradually matured. In addition to base stations and artificial satellites, digital television signals may also be transmitted through cable wires. The Digital Video Broadcasting-Cable (DVB-C) is one current common standard. For a DVB-C system, external interference frequently occurring in the signal transmission process includes impulse interference, adjacent channel interface and co-channel interference. In order to correct retrieve an input signal, a DVB-C receiver end needs to eliminate the effect that the above types of interference has on signal contents.
FIG. 1 shows a typical impulse interference eliminating apparatus. As shown in FIG. 1, an impulse interference eliminating apparatus 100 includes an impulse interference detecting circuit 12 and an impulse interference eliminating circuit 14. The impulse interference detecting circuit 12 detects whether impulse interference exists in an input signal Sin, and generates an impulse interference eliminating request Re only when having detected that impulse interference exists in the input signal Sin. According to whether the impulse interference eliminating request Re is received, the impulse interference eliminating circuit 14 determines whether to perform an impulse interference eliminating process on the input signal Sin to generate an output signal Sout. More specifically, only when the impulse interference eliminating circuit 14 receives the impulse interference eliminating request Re, the impulse interference eliminating circuit 14 performs an impulse interference eliminating process on the input signal Sin. Thus, the output signal Sout of the impulse interference eliminating circuit 14 is different from the input signal Sin. On the other hand, when the impulse interference eliminating circuit 14 does not receive the impulse interference eliminating request Re, the impulse interference eliminating circuit 14 does not perform the impulse interference eliminating process on the input signal Sin. Thus, the output signal Sout of the impulse interference eliminating circuit 14 is identical to the input signal Sin.
However, apart from impulse interference, adjacent channel interference and co-channel interference may simultaneously occur in the input signal Sin. An input signal mixed with multiple types of interference may cause misjudgment of the impulse interference detecting circuit 12. That is, the impulse interference detecting circuit 12 may regard non-impulse interference as impulse interference, such that the impulse interference eliminating circuit 14 may be mislead to erroneously perform an impulse interference eliminating process on the input signal Sin.
Erroneously triggering the impulse interference eliminating circuit 14 may cause undesirable effects on other performances on a system corresponding to the impulse interference eliminating apparatus 100. For example, the impulse interference detecting circuit 12 and the impulse interference eliminating circuit 14 may be disposed at a signal receiver end, and the impulse interference eliminating circuit 14 may be a Reed-Solomon decoder. The input signal Sin of the signal receiver end may include multiple packets. Each of the packets includes multiple symbols, which may include one or multiple erroneous symbols with known positions and/or one or multiple erroneous symbols with unknown positions. The impulse interference detecting circuit 12 notifies the Reed-Solomon decoder of the position of impulse interference in the input signal Sin detected, and the symbol occurring at that position is regarded as an erroneous symbol with a known position. The Reed-Solomon decoder then accordingly corrects the erroneous symbol with the known position and other erroneous symbols with unknown positions to decode the packet. However, the Reed-Solomon has a limited error correction capability. More specifically, as the number of erroneous symbols with known positions gets larger, the number of erroneous symbols with unknown positions the Reed-Solomon decoder can correct gets smaller. If the number of erroneous symbols with unknown positions exceeds the number of symbols the Reed-Solomon decoder can correct, the packet may not be successfully decoded and become an erroneous packet. It is known that, if the impulse interference detecting circuit 12 misjudges non-impulse interference as impulse interference, and the non-impulse interference does not in fact cause an error in the symbol at the position of the interference, the misjudged non-impulse interference may consume the error correction capability the Reed-Solomon decoder could have used for correcting erroneous symbols with unknown positions, hence resulting in an increased packet error rate in the output signal.